In a coder of a codec structure, for example a CELP (Code-Excited Linear Prediction) codec structure such as ACELP (Algebraic Code-Excited Linear Prediction), an input speech or audio signal (sound signal) is processed in short segments, called frames. In order to capture rapidly varying properties of an input sound signal, each frame is further divided into sub-frames. A CELP codec structure also produces adaptive codebook and fixed codebook contributions of an excitation that are added together to form a total excitation. Gains related to the adaptive and fixed codebook contributions of the excitation are quantized and transmitted to a decoder along with other encoding parameters. The adaptive codebook contribution and the fixed codebook contribution of the excitation will be referred to as “the adaptive contribution” and “the fixed contribution” of the excitation throughout the document.